In order to make bubbles for a miniature bathtub, you will need Amazing Casting Resin, Triple Thick, micro marbles/decorative beads, a dollhouse tub, and a miniature rubber ducky. You can purchase it in hobby stores: e.g. Hobby Lobby. Open it. Mix it well, according to the package. Poor it into the dollhouse tub. Allow the resin to set. It takes about 1 minute.
Mix Triple Thick with marbles and beads. Mix it well. These will be your bubble. Place them on top of your hardened resin. Shape it well. This will harden really hard. You'll want to shape it with attention to the way bubbles normally cluster together. Add your rubber ducky. Allow it to harden overnight.